Dangerous WPW Syndrome

Report:

Atrial fibrillation

Rapid response 240-300/min

Anomalous (WPW) conduction, type ‘B’

Comment:

If the observed cycle lengths during atrial fibrillation are less than 0.25” (250 milliseconds sounds more ‘learned’ in this context), the patient is in trouble and requires EPS for ablation or surgery.

Characteristically, there are a few normal complexes present: one in aVR and two in Lead 2. In this setting the conduction tends to be completely anomalous or (typically only a few beats) completely normal. The fusion beats with discrete delta waves seen in sinus rhythm are quite rare.

Those who mistake this bizarre-looking rhythm for multiform VT and reach for xylocaine will occasionally be successful, even though they may feel silly afterwards. The treatment of choice used to be procainamide, 500 to 1000 mg IV if the patient is not in extremis, when only DC countershock will help. Now flecainide or amiodarone have replaced procainamide, probably because they are more often used in other settings as well.

Below (Fig 84a) is the sinus rhythm ECG showing, as expected from the AF trace, WPW ‘B’ conduction.